As a technique of this type, Patent Literature 1 discloses a battery-side connector 100 and a rack-side connector 101 for electrically connecting a plurality of battery units which are inserted into a receiving rack as shown in FIG. 26 of this application. The battery-side connector 100 is a connector to be attached to each of the battery units. The battery-side connector 100 includes a battery-side housing 102 and a pair of battery-side contacts 103. Each battery-side contact 103 is partially covered by a comb-shaped covering portion 104 to prevent electric shock. The rack-side connector 101 is a connector to be attached to the receiving rack. As shown in FIG. 27 of this application, the rack-side connector 101 includes a first housing 105, a second housing 106, which is floatable with respect to the first housing 105, and sets of three rack-side contacts 107. In the above structure, when the battery-side connector 100 is mated to the rack-side connector 101, each battery-side contact 103 electrically contacts the corresponding set of three rack-side contacts 107.